4-Carbamoy-5-hydroxyimidazol (SM-108; [2]) is a known compound, a synthetic method of which is described in J. Am. Chem. Soc., 74, 2892 (1952), and has been known to have potent antitumor activities as described in JP S53-32124 A. The clinical trial of SM-108 had been conducted by Sumitomo Pharmaceuticals Co., Ltd. in 1980s.

The clinical outcomes clearly revealed that SM-108 shows excellent effects against myelodysplastic syndrome (MDS) and chronic myelocytic leukemia (CML) with reduced side effects such as myelosuppression action. However, the development of SM-108 as a chemotherapeutic agent was discontinued partly because of its chemical instability. SM-108 tends to produce a blue colorant by the air-oxidation. Although the drug formulation to improve the storage stability of SM-108 had been attempted by adding antioxidant agents as described in JP S58-35115 A, those efforts are far from the ideal method to overcome the problem efficiently.
On the other hand, MDS, the main target disorder of SM-108, is still categorized in a poor-prognotic syndrome and the number of patients is increasing gradually, especially in Europe and the United States. However, there is no efficacious therapeutics yet. Under these circumstances, the development of a new SM-108 derivative, which has improved storage stability, has been strongly desired.